1. Field of the invention
The present invention relates generally to an air conditioner. More particularly, the present invention relates to the structure of a heat exchanger arranged in the air conditioner.
2. Description of the Related Art
FIG. 25 is a vertical sectional view which shows a conventional air conditioner. Referring to the drawing, a suction grille 2 is formed on the front surface of a housing 1 as an air suction port. An air blow-off port 3 is formed on the lower part of the housing 1. An air passage 4 is formed so as to communicate the suction grille 2 with the air blow-off port 3. A filter 5 is disposed at the rear stage of the suction grille 2 and across the air passage 4. In addition, a heat exchanger 6 is disposed at the rear stage of the filter 5 and across the air passage 4. Further, a blower 7 is arranged at the rear stage of the heat exchanger 6 in the air passage 4, and a drain receiver 8 is disposed below the heat exchanger 6. In the drawing, an arrow mark A shows the flowing of external working fluid, e.g., air. Although not shown, a plurality of vanes are rotatably disposed in the air blow-off port 3 so as to redirect the flow of air.
FIG. 26 is perspective view of a heat exchanger for a conventional air conditioner, and FIG. 27 is a plan view which shows a plate fin for the conventional heat exchanger. The heat exchanger 6 is constructed such that a single heat conduction pipe 9 is turned several times and a large number of plate fins 10 are fixedly held in parallel with each other with a predetermined pitch in the axial direction of the heat conduction pipe 9. A plurality of cut-up pieces 10a are formed on each plate fin 10. Here, a copper pipe having a circular sectional shape and a diameter of 6 mm to 12 mm is used for the heat conduction pipe 9, and an aluminum plate is used for the plate fin 10. A working fluid B is caused to flow through the heat conduction pipe 9.
Next, a mode of operation of the conventional air conditioner will be described below.
When the blower 7 is driven, air A in the room is introduced into the housing 1 from the suction grille 2, passes through the air passage 4 and is blown off from the air blow-off port 3 into the room. At this time, when the air A passes through the filter 5 disposed across the air passage 4, dust is removed from the air A. And then, when the air A passes through the heat exchanger 6, heat exchanging is effected between the air A and the working fluid B flowing through the heat conduction pipe 9 to cool or heat the interior of the room.
With the conventional heat exchanger 6, as shown in FIG. 28, an air-temperature boundary layer C is cut, attributable to a front edge effect with the aid of the cut-up pieces 10a of the plate fin 10 when the air A passes by it. By cutting the air-temperature boundary layer C, heat conduction performances are elevated, resulting in performances of the air conditioner being improved.
FIG. 29 is a vertical sectional view of another conventional air conditioner, and FIG. 30 is a plan view of a plate fin used for the air conditioner. A plurality of holes 11a are formed through the plate fin 11 so as to allow heat conduction pipes 9 to be inserted therethrough, and cutouts 11b are formed on the plate fin 10 at plural locations. The plate fin 11 is bent at the cutouts 11b so that the heat exchanger 6A exhibits a contour having bent parts. In addition, another suction grille 2 serving as an air suction port is formed also through the upper surface of the housing 1, and a filter 5 and a heat exchanger 6A are arranged in the housing 1 to hinder the flowing of air sucked through the grilles 2 formed through the fore surface and the upper surface of the housing 1.
With the conventional heat exchanger 6A, a heat conduction area is increased attributable to the bent contour to enhance performances of the air conditioner.
To enhance the performances of the conventional air conditioner, the following measure are hitherto taken. Specifically, one of them is to improve heat conduction performances of the heat exchanger. Other one is to increase an area of the heat exchanger. Another one is to reduce an air pressure loss of the heat exchanger to increase a quantity of air passing past the heat exchanger.
With the conventional heat exchanger 6, by cutting the air-temperature boundary layer C attributable to the front edge effect with the aid the cut-up pieces 10a formed from the plate fin 10, heat conduction properties are improved to enhance the performances of the heat exchanger. However, formation of the cut-up pieces 10a from the plate fin 10 leads to the result that an air pressure loss is increased. Thus, in the case that this heat exchanger is incorporated in the air conditioner, a quantity of air flowing is reduced with the same power consumed by the blower 7. Consequently, there arises a problem that an effect for enhancing the performances of the air conditioner is reduced.
In addition, since the heat exchanger 6 has high rigidity due to the structure of the heat conduction pipes 9 and the plate fin 10 assembled together, the air conditioner has design flexibility. To increase a conduction surface by bending, the cutouts lib should be formed by cutting out a part of the plate fin 11 like the heat exchanger 6A. In this case, there arises other problem that the air conditioner is fabricated at an increased cost. Increasing of the conduction area of the heat exchanger leads to the result that the housing 1 is designed with large dimensions, i.e., the air conditioner is designed with large dimensions. In addition, unless a size of the housing 1 is changed, there is a limit for increasing a heat conduction area.
With the heat exchangers 6 and 6A, the plate fins 10 and 11 are dimensioned to have width of 10 mm or more to increase a heat exchange area. However, widening of the width of the plate fins 10 and 11 leads to the result that the housing 1 is designed with large dimensions. Thus, there arises another problem that the air conditioner is designed with large weight and fabricated at an increased cost.
In addition, with the heat exchangers 6 and 6A, since the structure of the whole heat exchanger is uniformly designed, pressure loss on the air side is equalized at the front surface, an air speed is reduced at the lowermost end part of the heat exchanger as well as at the part including no suction grille, and the air speed is fastened at other part rather than the foregoing ones. Consequently, the heat exchanger is not effectively used, performances of the air conditioner are degraded, and moreover, noise is generated from the air conditioner.
FIG. 31 is a perspective view of a conventional heat exchanger as disclosed on an official gazette of Japanese Patent Laid-Open Publication NO. 61-153388, and FIG. 32 is a sectional view of the heat exchanger shown in FIG. 31. A plurality of heat conduction pipes 12 are arranged in parallel with each other with a predetermined distance between adjacent ones, and a fine wire 13 is arranged between adjacent heat conduction pipes 12 along the surface of these heat conduction pipes 12 so that the fine wire 13 is knitted like Japanese mat on the assumption that each heat convention pipe 12 serves as a warp and the fine wire 13 serves as a welt. In the drawings, reference character A denotes an external working fluid, while reference character B denotes a internal working fluid.
In FIG. 32, the flowing state of the external working fluid A is shown by arrow marks. When the fluid A collides against the fine wire 13, the flowing state of the fluid A is disturbed, and the fluid A located below the fine wire 13 flows in the transverse direction along the fine wire 13 as shown by arrow marks while rising up on the surface of the heat conduction pipe 12. As a result, the time when the fluid A comes in contact with the heat conduction pipe 12 is increased.
In this case, since the fine wire 13 has a very small diameter, it comes in contact with the heat conduction pipe 12 with a small contact area. For this reason, the contact area between the fluid A and the heat conduction pipe 12 is not reduced by the fine wires 13, causing a heat conduction function to be effectively practiced.
In this conventional example, since each fine wire 13 has a circular or elliptical sectional shape, the contact part with the heat conduction pipe 12 exhibits an arc-shaped contour so that point contact or line contact occurs between the fine wire 13 and the heat conduction pipe 12. Thus, a contact area between the fluid A and the surface of each heat conduction pipe 12 is not reduced by the fine wire 13. Thus, a heat exchanger having a high heat exchanging efficiency is obtainable.
However, since this conventional heat exchanger has a small width of 1 to 3 mm, although it has large heat conductivity compared with the heat exchanger including the plate fin 10 around the heat conduction pipe 9 as shown in FIG. 26, since the heat conducting area is small as 1/10 or less, there arises a problem that a necessary quantity of heat exchanging can not be obtained.
In the case that the temperature of the external working fluid (e.g., refrigerant) is lower than a dew temperature of air, moisture in the air becomes dew droplets. At this time, dew droplets are held between the fine wires so that the space between the fine wires 13 is clogged with dew droplets. Since air does not sufficiently past the fine wires 13, a quantity of air flowing is reduced due to pressure loss. Thus, there arises a problem that a necessary quantity of heat exchanging is not obtained.